Neisseria gonorrhoeae is the causative agent of gonorrhea;humans are their only natural host. Neisseria can disseminate from the mucosal surface to cause severe diseases. Sexually transmitted infections, including gonorrhea, cause substantial morbidity in the United States, with about 600,000 new infections each year. Among women, many of these infections do not produce recognizable symptoms until after complications arise. Cases of pelvic inflammatory disease can result in infertility and ectopic pregnancy. Localized infections require the adherence and penetration of bacteria into epithelial cells. Many molecular determinants have been implicated in gonococcal pathogenesis such as porin, pili, lipooligosaccharide (LOS) and colony associated opacity proteins (Opa). Understanding how these molecules aid in the pathogenesis of the disease is the subject of ongoing research. The role of Opa proteins has been studied and the data suggest that they are involved in adherence to and invasion of epithelial, endothelial and phagocytic cells. Their importance in cellular tropism and their ability to promote transcytosis of epithelial cells has also been suggested. However, due to the phase and antigenic variability of opa genes, the specific function of each Opa protein in these processes has been difficult to elucidate. The central hypothesis of this research proposal is that expression of a distinct gonococcal surface antigens are important for the different stages of infection and with a particular disease outcome. Gonococci expressing different Opa proteins or none will have a different fate when encountering epithelial host cells, and this will allow GC to produce an array of diseases. In order to determine the role of each Opa variant, it is necessary to compare the interaction of gonococci expressing no Opa proteins with epithelial cells to those expressing one single-Opa protein. I propose to determine if variations in gonococcal Opa expression cause differences in attachment, invasion and transcytosis of epithelial cells. The results from this research will aid in the understanding of the role of Opa proteins during interactions with epithelial cells and how these antigens can affect the pathogenesis difference seen in symptomatic and asymptomatic cases. In addition, it will give an insight to new approaches for prevention and treatment of gonorrhea, as well as to give an insight into other pathogens that might use the same type of interaction with epithelial cells.